Switching arrangement for load change-over switches of step switches and for selector switches

ABSTRACT

The invention concerns a switching arrangement for load change-over switches of step switches and for selector switches, wherein two switching contacts movable in two directions are present. The first switching contact is in the form of a main switching contact and is connected to the load derivation by means of a first vacuum switchgear cell. The second switching contact is in the form of a resistance switching contact which is likewise connected to the load derivation by means of a series connection comprising a second vacuum switchgear cell and a transition resistor. Both the main and the resistance switching contacts can be moved independently of one another and without mutual coupling or influence. The main switching contact always reaches the new fixed contact abruptly and independently of the switching direction before the resistance switching contact leaves the previous fixed contact.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US national phase of PCT applicationPCT/EP95/00855 filed 8 Mar. 1995 with a claim to the priorities ofGerman patent application P 44 07 945.1 filed 9 Mar. 1994 and P 44 41082.4 filed 18 Nov. 1994.

1. Field of the Invention

The invention relates to a switchover arrangement for load switches oftap changers and for load selectors. Such a switchover arrangement isknown from German published application 2,520,670.

2. Background of the Invention

The known switchover arrangement of the German document has at least twobidirectionally movable switch contacts serving to switch a load outputline from one to another tap contact, one switch contact serving as amain switch contact and the other as a switch contact resistance, withboth resting in stationary condition on the same tap contact. Themovable switch contacts are thus fixedly coupled together and mounted ona common contact carrier and are also jointly actuated by movement ofthe common contact carrier. Independent of the switching direction onecontact always leads and the other follows.

Each of the movable switch contacts is in series with a mechanicalseries contact and the two series contacts are simultaneously andindividually connectable with the load output line. This selectableconnection is effected by a movable mechanical interrupting orswitchover contact. In addition, with this known arrangement aforce-storage unit is provided that, when tripped, actuates not only thetwo movable mechanically interconnected switch contacts as well as theinterrupter contact.

These known switchover arrangements have several disadvantages. First,they always require a mechanical interrupter contact. Vacuum switchingtubes, which are known for their fire-resistance and the resultantavoidance of fouling of the surrounding environment as well as for thelarge number of switch operations possible, cannot be used for the knownswitchover apparatus. In addition the switch contacts reverse theirmechanical functions depending on switching direction from leading totrailing; the switch cycle changes with the switching direction. Bothswitch contacts must therefore be actuated jointly by the force-storageunit and in addition the force-storage unit must as described actuatethe movable interrupter contact which forms the current connection tothe load output line so that the result is, in general, a complicatedmechanism and requires a correspondingly mechanically expensiveforce-storage unit.

OBJECT OF THE INVENTION

It is an object of the invention to provide a switchover arrangement ofthe above-described type that is usable for load switches and also forload selectors, which permits the use of vacuum switch tubes in the mainand in the resistance branch, and which has a kinematically simplemechanism and thus an uncomplicated force-storage unit working in bothdirections and only making an always identical switch step for actuatingthe least possible switchover means.

SUMMARY OF THE INVENTION

This object is achieved by a switchover arrangement for load switches oftap changers and for load selectors with at least two fixed tap contactsand with two bidirectionally movable switch contacts switching a loadoutput line from one fixed stepped contact to another fixed tap contact.The switching of the switch contacts is triggered by the springlikerelease of a force-storage unit. One of the switch contacts is formed asa main switch contact connected directly with the load output line,while the other switch contact is connectable as a resistance switchcontact in series with a switchover resistor to the load output line.The switch contact connectable as main switch with the load output linereaches the new fixed tap contact before the switch contact connectableas resistance switch contact with the load line leaves the previousfixed tap contact. According to the invention, both switch contactsbeing movable independently of each other without mechanical coupling orinterconnection. One of the switch contacts being connected in permanentseries contact with the switchover resistor so that independently of theswitching direction always the same first switch contact is connecteddirectly as the main switching contact and the second contact is alwaysconnected as the resistance switchover contact with the load outputline. The connection of both the first switch contact acting as the mainswitch contact as well as the second switch contact acting as theresistance switch contact with the load output line is made by means oftwo separate and separately actuatable vacuum switches. Only the firstswitch contact acting as main switch contact is directly actuated by thespring-like force-storage unit.

At least one mechanical continuous main switch can also be provided andwhich in stationary condition shunts the first switch.

The resistance switch contact can be movable in a springlike manner sothat a two-stage force-storage unit first actuates the main switchcontact and then with a time delay the resistance switch contact.

The resistance switch contact is movable in a spring like manner suchthat its movement is effected by a second force-storage unit trippedwith a time delay.

The main switch contact and the resistance switch contact can becoaxially pivoted and the fixed tap contacts arranged in axially andperpendicular or radial direction so that they can be swept overindependently of each other.

The main switch contact and the resistance switch contact are guidedlinearly independently of each other such that all fixed tap contactscan be swept over by both independently of one another.

Both the main switch contact and the resistance switch contact can eachbe formed by two coupled-together individual breaker contacts, onerespective individual breaker contact both of the main switch contact aswell as of the resistance contact being electrically connected with thefirst tap contact and the other individual breaker contact of both themain switch contact as well as of the resistance switch contact beingelectrically connected with the second fixed tap contact.

The individual breaker contacts of the main switch contact can beswitched by a first reversing switch and the individual breaker contactsof the second switch contact by a second reverser switch.

It is particularly advantageous with the switchover arrangementaccording to the invention that with it the slightest possible switchloading is achieved. It is therefore possible to provide for safetyreasons against the possible and statistically unignorable failure of avacuum switch tube, a mechanical series emergency switching branch whichcan be provided in any event in the switchover arrangement according tothe invention for a load selector and which can be monitored in aparticularly simple manner by a known optoelectronic arc detector withload-switch extinguishing when needed. In addition as a result of themodest load switch loading of the switchover arrangement according tothe invention it can be built with smaller and correspondingly cheapervacuum switch tubes. A particular advantage of the switchoverarrangement according to the invention is further that the separateactuation of the main switch contact on the one hand and of theresistance switch contact on the other hand allows for provision of along switching path which is significant with respect to the spacing ofthe contact elements and thus of the achievable voltage stability asalso with respect to the reseizing voltage when the emergency switchingshunt is used. It is significant for the switchover arrangementaccording to the invention that, independent of the switching directionand thus of the movement (rotation) direction of the drive, the mainswitch contact is always actuated first in a spring-like manner.

German patent 756,435 describes in principle that on direction change ofthe contact movement of the step selector contacts the selector contactconnected to the switchover resistor "passes" the other, but in thisknown solution both step selector contacts, i.e. the selector arms, aremechanically connected to each other and with the drive. The "passing"takes place either mechanically by a lost motion in the drive mechanismor electrically by two additional reversing switches which reverse theorientation, i.e. the switching of the step selector contacts onrotation-direction reversal. In the switchover arrangement according tothe invention, by contrast, both contact arms move fully independentlyof each other. The main switch contact is moved spring-like by thetripped force-storage unit to the new fixed contact and the resistanceswitch contact follows with a selectable speed.

It is already known from WO 94/02955 for load selectors to have twoselector arms that are independent of each other and movable without amechanical interconnection. With this solution the resistance contact ismoved slowly and continuously by the drive shaft toward the new contactwhile loading a force-storage unit and the switch contact follows thismovement in a spring-like manner after tripping of the force-storageunit. The arrangement described there is however only suitable for loadselectors. In addition this known arrangement for load selectors isknown for high switch loading which makes essential additional means inexcess of the emergency switching shunt in order to provide sufficientsafety in spite of the statistically undeniable possibility of thefailure of vacuum switch tubes. With the discussed switch loads withsuch arrangements it is also necessary to provide two vacuum switchtubes in series in the load branch which are preferably simultaneouslyactuated. This on the one hand increases the switch cost and alsonecessitates additional mechanical means for simultaneously actuatingboth vacuum switch tubes.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become morereadily apparent from the following description, reference being made tothe accompanying drawing in which:

FIG. 1 is a diagram which shows a first switchover arrangement accordingto the invention as part of a load switch;

FIG. 2 is a diagram which shows this first switchover arrangementaccording to the invention as part of a load selector;

FIG. 3 is a sequence diagram which shows in this first switchoverarrangement the steps necessary from one voltage level to another;

FIG. 4 is a timing diagram which shows the switching diagram for thisfirst switchover arrangement for multiple tap changing;

FIG. 5 is a view similar to FIGS. 1 and 2 which shows a secondswitchover arrangement according to the invention as part of a loadswitch;

FIG. 6 is a sequence diagram which shows in this second switchoverarrangement the necessary switching steps from one voltage level toanother;

FIG. 7 is another diagram which shows a third switchover arrangementaccording to the invention as part of a load switch;

FIG. 8 is a sequence diagram which shows in this third switchoverarrangement the necessary steps from one voltage-level to another andback again; and

FIG. 9 is a timing diagram which shows the switching diagram for thisthird switchover arrangement.

SPECIFIC DESCRIPTION

The switching cycles of the first switchover arrangement according tothe invention are essentially the same independent of whether thisswitchover arrangement is part of a load switch or part of a loadselector. The sole difference is that a load selector can be steppedthrough several positions while a load switch moves mainly between twopositions so that each time the switching direction is reversed.

The switchover arrangement shown in FIG. 1 has two fixed tap contacts A,B which are connected in the known manner via a step selector with tapsn, n+1, n+2. . . of the step winding.

The actual switchover arrangement moves between these contacts A and B.This consists of a main switch contact SKM which is connected via afirst vacuum-switch cell SKV with a common output line as well as of aresistance switch contact HKM which is independent and mechanicallydecoupled therefrom and connected in series with a second vacuum-switchcell HKV and a switchover resistor R to the common output line. Inaddition in this embodiment there are preferably continuous mainswitches DHK_(A) and DHK_(B) which in stationary use conduct the loadcurrent and thus bypass the switchover arrangement. These continuousmain switches are not strictly necessary for the operation of theswitchover arrangement, so that load current can, when the vacuum-switchcells are appropriately dimensioned, be conducted also by the mainswitch contact SKM and the first vacuum-switch cell SKV, which is closedin stationary operation, in series therewith.

FIG. 2 is a diagram which shows this first switchover arrangement as apart of a load selector, where the continuous main switches are notstrictly necessary; the differences between actuation of the switchoverarrangement as part of a load switch on the one hand of a load selectoron the other hand have already been given.

FIG. 3 is a diagram which shows in the first switchover arrangement thenecessary steps from one voltage level to another. These steps areindependent of whether the switching is from a lower to a higher voltagelevel or vice versa. The individual steps are is a diagram which showsat 1 through 11.

Step 1: Starting position, DHK_(A) conducts the load current.

Step 2: DHK_(A) has opened, the main switch contact SKM and the firstvacuum-switch tube SKV have taken over the load current.

Step 3: The first vacuum switch tube SKV has opened, the load currentflows through the resistance switch contact HKM, the second vacuumswitch tube HKV, and the switchover resistor R.

Step 4: The main switch contact SKM leaves the fixed contact n or Aafter tripping of a force-storage unit.

Step 5: The main switch contact SKM reaches the new fixed tap contactn+1 or B.

Step 6: The first vacuum switch cell SKV closes and switches the loadcurrent to the fixed tap contact n+1 or B; the still closed secondvacuum switch cell HKV and the switchover resistor R conduct only thedifferential current.

Step 7: The second vacuum switch cell HKV opens and interrupts the flowof the differential current.

Step 8: The resistance switch contact HKM leaves the fixed tap contact nor A and follows the movement of the main switch contact SKM to the newfixed tap contact n+1 or B.

Step 9: The resistance contact HKM has reached the new fixed tap contactn+1 or B.

Step 10: The second vacuum switch cell HKV closes.

Step 11: The continuous main switch DHK_(B) closes and takes over theload current. The starting position has been reached and the switchoverarrangement is ready to be switched again.

It is clear that there is no addition of load and differential current,only a slight loading on switching.

It is thus clear that independently of whether one is moving to a higheror a lower voltage level, the main switch contact SKM moves rapidlyfirst and the resistance switch contact HMK follows rapidly. It is thusnecessary to actuate the main switch contact SKM rapidly by a trippedspring force or other energy-storage unit 10. The following resistanceswitch contact HKM can theoretically also follow slowly or continuouslybut this eliminates one of the advantages of the invention, that is thesimple monitoring of the vacuum switch tubes by a mechanical emergencyswitching shunt. This emergency circuit is only possible when theresistance switch contact HKM follows rapidly. This rapid movement ofthe following resistance switch contact HKM is possible by means of atwo-part force-storage unit 11 or two interconnected force-storage unitsso that after tripping of a first force-storage unit and movement of themain switch contact SKM with a time delay a second force-storage unit istripped which causes the resistance switch contact HKM to follow.

FIG. 5 is a diagram which shows a second switchover arrangementaccording to the invention which is specially set up for load switcheswhere as described one only moves between two fixed contacts A and B. Asa particularly advantageous feature of the invention the main switchcontact SKM as well as the resistance switch contact HKM each consist oftwo interconnected and coupled individual breaker contacts SKM_(A),SKM_(B) and HKM_(A), HKM_(B), each individual contact SKM_(A) andHKM_(B) being electrically connected with the first tap contact A andthe other individual breaker contacts SKM_(B) and HKM_(B) beingelectrically connected to the other tap contact B. In this embodiment ofthe invention there are thus two double interruptions; in this manner asimple load switching is possible during switchover in which only simpleinterrupters, contact bridges or the like are necessary as mechanicalswitch elements.

FIG. 6 is a diagram which shows the appropriate switching cycle. It isclear that here permanent connections are merely closed or opened fortransmitting the load through the respective individual breakercontacts.

FIG. 7 is a diagram which shows a third embodiment of a switchoverarrangement according to the invention. This embodiment is also set upspecially for load switches where once again the switching only takesplace between two fixed tap contacts A and B. The furtherabove-described individual breaker contacts SKM_(A), SKM_(B) of the mainswitching circuit SKM as well as the individual breaker contacts HKM_(A)and HKM_(B) of the resistance switch contact HKM are here switched bytwo reversing switches S1 and S2. The first reversing switch S1selectively closes the individual breaker contact SKM_(A) or theindividual breaker contact SKM_(B). Here there is thus a doubleinterruption by means of four individual breaker contacts which are in aspecial manner switched by only two reversing switches S1 and S2.

FIG. 8 is a diagram which shows the switching cycle from the fixed tapcontact A to the fixed tap contact B and back again. One can see thateven in this embodiment the main switch contact reaches the new fixedcontact B, that is to connect same with the load output line L directly,before the resistance switch contact leaves the previous fixed tapcontact, that is before the previous connection via the switchoverresistor R with the load line L is broken. It is further clear that inall described embodiments of the invention the movement or the actuationof the main switch contact on the one hand and the resistance switchcontact on the other hand takes place without a mechanicalinterconnection. Even in the last-described embodiments it is alsopossible to provide additional continuous main switches which in astationary condition transmit the main current flow.

We claim:
 1. An under-load switch comprising:two spaced apart fixedcontacts connected in an electrical circuit and selectively connectableunder load; a main switch contact and a resistance switch contactconnected to a load mechanically decoupled from one another and movableindependently from one another bidirectionally between said fixedcontacts so that, independently of direction of movement, said mainswitch contact always engages a fixed contact to be selected before theresistance switch contact engages the fixed contact to be selected; aswitchover resistance in series with said resistance switch contact andbetween said resistance switch contact and said load; a main vacuumswitch cell connected in series with said main switch contact betweensaid main switch contact and said load, and a resistance vacuum switchcell connected in series with said resistance switch contact betweensaid resistance switch contact and said load, said vacuum switch cellsbeing selectively rendered conductive and nonconductive independently ofone another; and a first force storing unit connected to said mainswitch contact and a second force-storing unit connected with saidresistance switching unit for:tripping of said first force storing unitto jump said main switch contact into engagement with the fixed contactto be selected before said resistance switch contact leaves a priorfixed contact, and thereafter tripping of said second force storing unitafter a time delay to jump said resistance switch contact intoengagement with said fixed contact.
 2. The underload switch defined inclaim 1 wherein said main switch contact and said resistance switchcontact are displaceable about a common axis and said fixed contactsextend in at least one of an axial direction and a radial direction sothat said main switch contact and said resistance switch contact can bemoved into engagement with said fixed contacts independently.
 3. Theunderload switch defined in claim 1 wherein said main switch contact andsaid resistance switch contact are displaceable independently from oneanother linearly and said fixed contacts are so arranged and constructedthat they can be independently swept over by said main switch contactand said resistance switch contact.
 4. An under-load switchcomprising:two spaced apart fixed contacts connected in an electricalcircuit and selectively connectable under load; a main switch contactand a resistance switch contact connected to a load mechanicallydecoupled from one another and movable independently from one anotherbidirectionally between said fixed contacts so that, independently ofdirection of movement, said main switch contact always engages a fixedcontact to be selected before the resistance switch contact engages thefixed contact to be selected; a switchover resistance in series withsaid resistance switch contact and between said resistance switchcontact and said load; a main vacuum switch cell connected in serieswith said main switch contact between said main switch contact and saidload, and a resistance vacuum switch cell connected in series with saidresistance switch contact between said resistance switch contact andsaid load, said vacuum switch cells being selectively renderedconductive and nonconductive independently of one another; and a forcestoring unit connected to said main switch contact, the main switchcontact and the resistance switch contact each being comprised of a pairof coupled and commonly actuated breaker contacts capable ofsequentially making and breaking an electrical circuit for therespective switch contact and positioned so that one of said breakercontacts of the main switch contact opens a connection with a priorfixed contact before a second breaker contact of said main switchcontact closes on a fixed contact to be selected and a first breakercontact of said resistance switch contact opens at said prior fixedcontact before a second breaker contact of said resistance switchcontact closes on said fixed contact to be selected.
 5. The underloadswitch defined in claim 4 wherein the breaker contacts of each pair areprovided on respective rotary switches.